The use of aluminum and steel sheet piling, as well as the use of treated timber, to include timber beams and planking, in constructing retaining walls, sea walls, and the like is well known. Aluminum and steel sheet piling has the advantage of being rigid, however aluminum and steel sheet piling is expensive, and over time, particularly when exposed to the elements, the aluminum and steel will corrode such that retaining walls formed of these sheet pilings need to be periodically maintained, and/or replaced. Treated timber on the other hand, tends to be less expensive and thus more cost effective than aluminum and/or steel sheet pilings, and may provide a satisfactory service life dependent upon the usage for which the retaining wall is constructed. However, a problem that arises with the use of treated timber is that it has been banned in a great many areas due to its toxicity, and treated timber is experiencing substantially reduced service life due to increased marine borer activity.
Due to the aforementioned problems or using aluminum, steel, or treated timber retaining walls, the use of plastic or vinyl extruded sheet piling has become a popular option for use in forming retaining walls and sea walls. Extruded vinyl and plastic sheet pilings offer the advantage of being lightweight, less expensive than steel sheet pilings, and can also be extruded in a variety of architectural shapes and styles for a greater blend of utilitarian purpose and aesthetics than is available with rolled steel sheet pilings. Examples of such plastic sheet pilings are disclosed in U.S. Pat. No. 4,690,588 to Berger; U.S. Pat. No. 4,863,315 to Wickberg, and U.S. Pat. No. 5,145,287 to Hooper, et al. U.S. Pat. No. 5,066,353 to Bourdo discloses a fiberglass sheet piling which offers the advantages of being less costly to fabricate than an extruded sheet piling, yet has the significant disadvantage of being more brittle such that if struck by a blunt force, for example a driftwood log if used in a sea wall, or by a vehicle if used to construct a retaining wall, the fiberglass panels could easily be cracked or destroyed.
Although plastic sheet pilings offer the advantage of being rugged, durable, inexpensive, and easy to use, they have the distinct disadvantage of being more flexible, i.e. having less structural rigidity than do steel sheet pilings. As known to those skilled in the art, a steel sheet piling will have a modulus of elasticity approximately 75 times greater than that of a plastic sheet piling. In most applications, the section thickness of an extruded sheet piling can be made thinner or thicker dependent on the end usage in which the sheet piling will be used, such that the disadvantage of a plastic sheet piling with regard to the structural rigidity of a steel sheet piling is minimized. However, in increasing the section thickness of an extruded plastic sheet piling, this necessarily results in increased costs and weight, which may impact the economic decision to use a plastic sheet piling in lieu of a steel sheet piling in the first instance. Three examples of an extruded plastic sheet piling based on the plastic panel erosion barrier disclosed in Hooper, et al are disclosed in FIGS. 1A-1C. These vinyl sheet pilings are also known as the ShoreGuard.RTM. family of vinyl sheet piling manufactured and sold by Materials International, Inc. of Atlanta, Ga.
As illustrated in FIGS. 1A-C then, three extruded sheet pilings 5, 5' and 5" are disclosed, each of which is constructed in an almost identical fashion, although they differ in terms of the geographic profile formed by the extruded sheet piling. Thus, each one of these three sheet pilings has an elongate planar body panel 7 having a first continuous side edge 8, and a second continuous side edge 9. Extending from the first side edge 8 is a first flat section, known to those in the industry as a flat, having a continuous male locking member 12 formed along its outside edge opposite the first side edge of the body panel. As shown in FIGS. 1A and IB, the male locking member 12 is situated at the end of an arcuate section 13 formed along the outside edge of the first flat 11.
The sheet piling of FIGS. 1A-C has a second flat section 15, known as a second flat, extending away from the second side edge 9 of the body panel. A complimentarily shaped female locking member 16 is formed along the length of an outside edge of the second flat opposite the second side edge of the body panel. The two flats 11 and 15 extend in directions opposite one another and away from body panel 7, and are positioned parallel to one another such that a reversible profile is formed, in which, for example, respective adjacent ones of the sheet pilings 5, 5', and 5" can be placed in top end to top end, or top end to bottom end interlocked edge-standing relationship with respective ones of the extrusions 5, 5', and 5".
As shown in FIGS. 1A and 1B, each male locking member 12 is formed as a generally T-shaped member, whereas the female locking member 16 is formed as a substantially C-shaped member. In the embodiment of FIG. 1C, however, the male locking member 12" is formed to have two outwardly projecting portions sized and shaped for being received within a substantially circular female locking member 16".
Although the embodiments of the prior art sheet pilings shown in FIGS. 1A-1C have proven to be a significant improvement over the sheet pilings and the vinyl plastic sheet pilings known in the art, the problem remains that due to the greater flexibility of an extruded plastic sheet piling, the flats 11 and 15 will tend to bend or deflect about a central bending axis or plane extending between the two flats in response to the application of a static or dynamic load or force against the flat. Although the interlocked edge-standing relationship of the male locking member within the female locking member of an adjacent sheet piling tends to add some structural rigidity to a plastic sheet piling retaining wall, the problem still exists that if an unexpected load is placed against the sheet piling the male locking member may be pulled out of the adjacent female locking member, and/or that the retaining wall could bow or flex, perhaps destructively so, dependent upon the loads being transmitted against the wall.
What is needed, therefore, but seemingly unavailable in the art is an extruded plastic sheet piling constructed and arranged to be placed into an interlocked edge-standing relationship with adjacent ones of the extruded sheet piling which will have a greater degree of structural rigidity than those extruded sheet pilings known in the art. What is also needed is such an improved sheet piling extrusion which will increase the strength of the interlocked male and female locking member joint to increase the pull-out strength of the interlocked male and female locking members. Additionally, there is a need for such an improved plastic sheet piling which will be balanced about its centroid such that the flow of the plastic material through an extrusion die is balanced, and so that the cooling of the extruded sheet piling will also be balanced about the centroid such that torsional forces which would otherwise tend to twist or flex the sheet piling extrusion as it cools will be greatly mitigated, if not eliminated entirely.